Maple Leaf Photonic
The Pioneer of Automated Photonics Integrated Circuit Testing

Semiconductor technology has been the cornerstone for innovation in computing for seven decades now. One of the more recent advancements has been the introduction of silicon-on-insulator (SOI) wafers into the manufacturing process. In addition to allowing more power-efficient and faster electronic circuits, the SOI platform also allows near-infrared (NIR) light to be confined and manipulated in small silicon wires, called waveguides, on chip. This technology, often referred to as silicon photonics, has caused a revolution in traditional optical-based systems. For example, high-speed data communications brought about by optical fiber networks and discrete photonics can now be integrated into a single, monolithic device called Photonic Integrated Circuit (PIC). PICs allow transistors (electrons) and photons (light) to be manipulated simultaneously, creating fast, complex systems in a small and power-efficient footprint. In the last decade, integrated photonics has fundamentally improved efficiencies in data centers by replacing copper wires with high-speed optical cables. Other markets, like quantum computing, LIDAR, and a wide range of sensing and healthcare applications have also reaped the benefits of integrated photonics as well.

The integration of light into CMOS chips has created unique test challenges for developers and manufacturers. CMOS chip designers can leverage established process design kits (PDKs) provided by foundries to build complex circuits. The design, verification, and test tools are mature and well understood, providing high confidence in realizing complex products the first time. This is not the case with photonic integrated circuits. Progress has been slow and little standardization exists for photonic integrated circuit-based design flows, including testing and characterization.

A basic and challenging aspect of PIC testing involves getting light on and off the chip and controlling the various instrumentation required for measurements. This is especially true for R&D environments where photonic designs are being realized for the first time and optimized prior to high-volume fabrication and testing. Manually aligning fibers and programming the bench-top laser sources, detectors, modulators, and analyzers to test optical circuits can take hours or days. Customizing traditional and existing CMOS test tools is either not possible or involves exponential costs, which is often prohibitive for R&D test budgets.

Maple Leaf Photonics has solved this issue with its family of innovative and customizable photonic probe stations. Their vision is to accelerate PIC development by lowering the barrier to entry for tests throughout the product design cycle. They accomplish this by solving the most costly and time-consuming tasks in PIC testing, namely aligning fibers to on-chip circuits and orchestrating automated tests involving bench-top test instrumentation.

“MLP was founded by silicon photonic designers who needed an efficient way to test their own PICs. We understand the challenges in PIC testing and focus on PIC R&D market. We work closely with customers to solve their most difficult test problems,” explains Shon Schmidt, CEO and co-founder of MLP.

MLP is the first company to introduce a fully automated single-die photonic probe station for less than $100k compared to the $300k+ price tag of traditional CMOS wafer probe stations. MLP achieves this through its custom-designed modules and controls that have been optimized for the R&D market and their unique PIC testing needs. The probe station consists of three parts: probe station hardware, a set of controllers, and the test automation software, called Fotonica®. The probe station hardware consists of the fiber positioners, the chip positioner, inspection cameras, and DC and RF probe positioners. The controllers provide motion, environmental and photonic signal path controls. The software communicates with the bench-top instruments, executes alignment algorithms, and orchestrates the automated tests. Users load die device coordinates into Fotonica® and once the die is registered, users can align to every device on the chip with high accuracy and repeatability, prerequisites for automated testing and trustworthy measurements.

The company has a family of products designed to meet a myriad of PIC testing needs. The system has been architected to allow customers to tailor probe stations for unique needs and evolve or scale-up existing probe stations as new needs emerge. The SD100 has been the company’s workhorse since its inception in 2015. Its fiber positioner supports both edge-or grating-coupled configurations and handles die up to 25x50 mm. Its modularity and flexibility make it a natural choice for R&D groups that require flexibility in their test setups. More recently, MLP launched the SD120, which extends the capabilities of the SD100 by reducing alignment time from approximately 30 seconds to 1 second for applications where test time is the most critical factor.

MLP also offers probe stations for specific applications as well. Its SD90 has been optimized for edge-coupled fibers and provides long-term stability for applications like PIC-based quantum computing that often require hundreds of DC biasing channels and dozens of edge-coupled optical IOs. The MD100, a multi-die probe station, tests several dies in sequence to confirm uniformity, quality, and assess performance metrics. This system helps qualify components as they ramp into production.

Users can extend and customize their probe station using Fotonica’s Application Program Interface (API). “Fotonica’s API allows a user to quickly integrate custom instruments or develop unique test sequences on the fly, adapting the probe station to their specific test needs. As the design matures, this R&D investment scales nicely to the production floor,” explains Schmidt.

MLP provides exceptional customer support. With each sale, engineers spend time onsite to assemble and calibrate the system. As part of this process, they provide system training with the customer’s device and instrumentation. This has been critical in developing each customer’s confidence with the probe station and measured results on their device. MLP offers a variety of support programs depending on the customer’s needs and Schmidt says providing post-sales support results in trust and deep relationships with each customer.

In the future, Maple Leaf will pursue two key tactics. Because testing PICs requires both precise probe stations as well as the latest test equipment, Maple Leaf will continue to offer open architecture and relationships with all the major test set vendors. As evidence of this tactic so far is the extensive list of Fotonica drivers for instrumentation from Exfo, Luna, Keysight, Okagawa, Santec, and many others. Secondly, new products will integrate machine learning and artificial intelligence to keep pace with the market needs for test speed and complete automation.